The front end structure of an automotive vehicle is designed to provide visual appeal to the vehicle owner while functioning as an energy absorbing structure during frontal and offset crashes. The size, shape and construction of the front end structure contribute to the ability of the front end structure to attenuate the crash pulse and restrict intrusions into the operator's cabin of the vehicle. It is important to design a front end structure to absorb crash energy through the most effective structural components, which is a front rail system. To that extent, a significant amount of effort by vehicle engineers is devoted to designing the front rails to crush in a controlled manner while absorbing a maximum amount of energy. If additional energy absorption is required, adding length to the front rails is the next logical engineering consideration. Even though longer front rails are desirable for efficient energy management, this option is usually commercially unacceptable to the vehicle customer because resulting structure is considered to be visually unattractive, increases the vehicle overall length and reduces vehicle parking maneuverability.
One of the goals in the design of vehicle frame structure is to provide better engagement and absorption of energy during a collision. The major components in absorbing energy in frontal as well as rear impacts are the rails. Furthermore, in a side collision if the vehicle has a softer front end it can help mitigate the injuries to occupants in both vehicles. If there is an apparatus to absorb more energy and prolong the time to crush the rails, the crash pulse and intrusion can be reduced significantly. With a longer front end structure on a vehicle, there is potential to achieve this goal. A secondary aspect to extending the front end structure is to localize less severe crash damage into a few local parts that are easily repairable or replaceable. A significant problem, however, is providing the extendible front end is to do so without changing other critical design aspects, such as styling and dimensions of a vehicle, that are critical to both the manufacturer and the customer.
Alternative engineering design can provide larger bumpers, deployable bumper airbags, and rails with pyrotechnique methods etc., which can have styling and packaging issues or require sensors to activate and can lead to high repair costs in the case of a false deployment of the known prior art systems. For these reasons, such alternative systems have not met with commercial acceptance. Accordingly, attempts have been made to provide a selectively extendible bumper structure that is operable to move the bumper from an aesthetically pleasing position to an extended position that positions the bumper at a significant distance from the retracted position. Such extendible bumper structures have been associated with a speed sensor such that the bumper extends automatically in response to the attainment of a preselected speed criteria.
One such extendible bumper structure can be found in U.S. Pat. No. 6,773,044, issued on Aug. 10, 2004, to John E. Schambre, et al, in which the front bumper is supported on telescopically extendible rails that move the front bumper forwardly when the vehicle reaches a predetermined speed. Drive cables and a worm gear assembly drive a ball screw cam into a locking mechanism inside the movable rail pieces. The locking links are driven outwardly by the ball screw cam to extend through slots aligned in the fixed and movable rail pieces so that crash forces can be transferred from the movable rail piece to the fixed rail piece during an impact.
The extendable rails disclosed in the Schambre patent are driven by a cable mechanism and a drive motor located inside the bumper. Accordingly, this bumper beam needs to be designed to have enough package space to house these components. Providing the space to house these components is an added design requirement for the bumper. The locking mechanism is one of the most critical components to manage energy during a frontal impact. The material that is removed in the fixed and movable rails to make slots for the locking links is significant. Locking links as disclosed in the Schambre patent need to be very strong and the resulting slot area becomes considerably large. As a result, the rail pieces become locally weaker at the slots and would have a tendency to bend during collision, especially when an offset impact is incurred.
Another extendible bumper structure is found in U.S. Pat. No. 6,709,035, issued to Chandra Namuduri on Mar. 23, 2004. The Namuduri extendable rail pieces are assembled inside a secondary casing which is mounted inside the base frame rail defining three sheet metal parts with closed cross sections at the front of the bumper when the rails are in a retracted position. The extendable rail travels inside the middle (secondary) rail casing which is rigidly attached to the outer frame rail. The actuating mechanism works with a lead screw that connects to a drive motor and a nut. The nut is connected to the inside end of the movable rail piece through a self-locking mechanism that works with a plurality of small spheres sliding on a tapered bushing. These spheres tightly constraint the extendable rail and the secondary casing during an impact.
The Namuduri bumper energy absorber for supporting the bumper structure relative to a vehicle includes an inner tube, an outer tube, a lead screw, a nut and a motor. Rotation of the lead screw by the rotor causes translation of the nut along the lead screw for driving at least a portion of the bumper structure between extended and retracted positions. When the extendable rail is moving outward and inward, respectively, a sensing and controller system is used to control the position of the two moving rail pieces. The degree of extension can be controlled by various parameters via sensors, including gear position, vehicle speed, obstacle range, approach rate and hard braking. With respect to crash energy management and efficiency of the system, having three tubes in the retracted position is not desirable and also add unnecessary weight and cost of manufacturing. The positioning of the motor mechanism installed inside the rails take up a considerable length and would not crush due to the many metal pieces in the motor, drive and the constraint mechanism. Furthermore, the movable rails need to be of a considerable size to adsorb a significant amount of energy during impact. Hence, the resulting complete mechanism becomes larger than a current front end and may not be suitable for vehicle design, especially for small vehicles.
U.S. Pat. No. 5,967,573, issued on Oct. 19, 1999, and related U.S. Pat. No. 6,302,458 issued on Oct. 16, 2001, and U.S. Pat. No. 6,401,565 issued on Jun. 11, 2002, all of which are issued to Jenne-Tai Wang, et al., disclose an extendible front bumper structure that actuates upon attainment of a pre-established speed criteria through a rack and pinion mechanism. The extendible rail structure is locked against the fixed rail structure by a plurality of small spheres that slide on a tapered bushing. These spheres deform the outer tube to absorb energy upon impact. U.S. Pat. No. 6,834,898, granted on Dec. 28, 2004, to Jenne-Tai Wang, et al, discloses similar structure having increased stiffness by mounting the actuator inside the tubular frame rail member. U.S. Pat. No. 6,976,565, granted to Paul Meernik et al, on Dec. 20, 2005, discloses a spring-loaded apparatus for absorbing energy in an extendible bumper apparatus as disclosed in the above-identified Wang patents.
Another configuration for an extendible bumper system can be found in U.S. Pat. No. 6,976,718, issued to Isumu Nakanishi on Dec. 20, 2005, in which an electric motor drives a threaded actuator rod to extend the front bumper from a retracted position to an extended position. The bumper apparatus incorporates an electromagnetic lock mechanism and a deformable, energy absorbing shaft to absorb impact forces encountered by the bumper apparatus.
It would be desirable to provide an extendible bumper for an automotive vehicle that incorporates a locking mechanism to transfer any crash forces encountered by the extended bumper to the frame of the vehicle. Such an extendible rail system would provide a rail extension apparatus and a control for extending the rails to improve crash energy management without affecting the visual appeal of the vehicle when stopped or at low speeds. The extendible rail system would be applicable to front or rear bumpers on an automotive vehicle.